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Stefano Mazzoli, Università di Napoli Federico II (Italy)
Luca Aldega, Università Roma 3 (Italy)
Alessandra Ascione, Università di Napoli Federico II (Italy)
Sveva Corrado, Università Roma 3 (Italy)
Marco D'Errico, Università di Napoli Federico II (Italy)
Alessandro Iannace, Università di Napoli Federico II (Italy)
Chiara Invernizzi, Università di Camerino (Italy)
Antonio Pignalosa, Università di Bologna (Italy)
Stefano Vitale, Università di Napoli Federico II (Italy)
Massimiliano Zattin, Università di Bologna (Italy)
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In southern Italy, subduction of the leading edge of the Adria continental margin is testified by HP-LT metamorphism affecting the Triassic to Lower Miocene rocks of the Lungro-Verbicaro Unit. The late stages of exhumation of these rocks are constrained by apatite fission-track data, showing cooling ages ranging between 11.6±1.1 and 8.9±1.4 Ma. These ages partially overlap with those from the sedimentary units occurring in the footwall and north of the HP-LT rocks, characterized by apatite fission-track ages ranging between 9.2±1.0 and 1.5±0.8 Ma. These units include both Mesozoic-Tertiary carbonate platform and pelagic basin successions, together with unconformable Miocene siliciclastics. Collectively, these rocks form a highly displaced allochthon that has been carried onto a footwall succession essentially continuous with that of the foreland Apulian Platform. The buried Apulian carbonates (6-8 km thick) are deformed by relatively low-displacement, high-angle reverse faults involving the basement. Therefore, a switch from thin-skinned to thick-skinned thrusting appears to have occurred as the Apulian carbonates - and the underlying thick continental lithosphere - were deformed. Apatite fission-track and U-Th/He data, showing cooling ages mainly comprised within the last 5 Ma, indicate that exhumation marks these late tectonic stages. Pliocene to Early Pleistocene foreland motion of the allochthonous units largely exceeded the total amount of slip that, based on cross-section balancing and restoration, could have been transferred from the buried Apulian carbonates to the overlying allochthon.
This suggests that emplacement of the allochthon on top of the foreland Apulian carbonates was followed by gravity spreading of the weak allochthonous wedge. Further evidence supporting the hypothesis that gravitational readjustments played a major role in tectonic evolution and related exhumation processes is provided by the high unloading rates that can be estimated based on apatite fission tracks and U-Th/He data. Furthermore, the sedimentary record coupled with morphotectonic evidence point to the occurrence of large collapses affecting the outer portion of the thrust belt, with the formation of wide wedge-top basins. These phenomena provided an important contribution to the attainment of the present shape of the thrust belt. The latter in fact features an asymmetrical shape, with the eastern slope displaying a lower dip lower than the western one, and maximum elevations mostly located to the west of the chain axis, in spite of the larger and faster Quaternary uplift experienced by the eastern slope.
Our model, emphasizing the role of gravity-driven processes interacting with thrust tectonics, sheds new light on this key area of the Alpine-Mediterranean region, and provides new insights into the evolution of fold and thrust belts.
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